2018 Audi S8 Wheel Interchange

OEM wheel/tire sizes and fitment specs for the 2018 Audi S8.

2018 Audi S8 wheel fitment guide

tl;dr

  • OEM baseline: 21x9.0 ET35 wheel with 275/35R21 tire.
  • Bolt pattern: 5x112. Center bore: 66.6 mm. Thread: M14 x 1.5.
  • Backspacing listed: 5.88 in. Measure yours to confirm.
  • Set “Installed on” to 2018 Audi S8 in the calculator, then compare donor or custom sizes before you buy.
  • Avoid guessing. Confirm in your owner’s manual, door jamb label, or with an Audi parts desk.

Recommendation

Start from the OEM envelope. Keep wheel width, offset, and tire diameter close to factory to preserve clearance, handling, and speedometer accuracy. Use hub-centric wheels or quality hub-centric rings sized to 66.6 mm. Match fastener thread to M14 x 1.5. If a wheel’s center bore is larger than 66.6 mm, rings are required. If it is smaller, the wheel will not seat.

Use the on-page calculator. Set “Installed on (your vehicle)” to 2018 Audi S8. Enter either a donor vehicle wheel or a custom size. Review inner clearance to the suspension and brakes, outer “poke” relative to the fender, and tire diameter change. Large S8 brakes need generous spoke and barrel clearance. If you are considering spacers for caliper clearance, ensure they are hub-centric and that hardware length matches any spacer thickness.

Impact of changes

  • Offset: More positive offset moves the wheel inward. Less positive moves it outward. The calculator will show inner clearance and poke changes.
  • Width: Wider wheels grow inward and outward from the centerline. Check both sides for contact risk.
  • Tire size: Changing section width or aspect ratio alters overall diameter. The calculator updates tire diameter and shows the difference vs OEM.
  • Center bore and hub fit: Anything smaller than 66.6 mm will not fit the hub. Larger needs rings to stay vibration free.
  • Hardware: The thread must be M14 x 1.5. Seat style can vary by wheel brand. Confirm with the wheel supplier.

Risks and gotchas

  • Brake clearance: The S8 has large front calipers. Test spoke and barrel clearance before final mounting.
  • Fender and liner rub: Check at full lock and during suspension compression. Air suspension changes ride height. Recheck at your lowest setting.
  • Load rating: Wheels and tires must meet or exceed vehicle load. Low ratings lead to failures.
  • TPMS: Sensor type and frequency may vary by market or trim. Inspect your current wheels and confirm with OEM documentation.
  • Spacers: Only use hub-centric spacers with correct hub and wheel bores. Hardware length must suit the spacer. Poor setup can cause vibration or loss of clamping force.
  • Backspacing variance: Published backspacing can differ from measured due to lip design. Measure if you are close on inner clearance.
  • Torque: Follow Audi’s specified torque and recheck after a short driving period. Do not guess values.
  • Alignment: Any fitment change can affect alignment needs. Plan for an alignment after installation.

OEM fitment reference

Spec2018 Audi S8
Bolt pattern5x112
Center bore66.6 mm
Thread sizeM14 x 1.5
Rim diameter21 in
Rim width9.0 in
Wheel offset (ET)35 mm
Backspacing5.88 in
Tire size275/35R21

If your car differs, it may be due to regional packages, brakes, or dealer-installed options. Confirm by VIN with an Audi parts department or your owner’s manual.

How to use the wheelinterchange.com calculator

  • Set “Installed on (your vehicle)” to 2018 Audi S8.
  • Enter the wheel and tire you plan to use under “Custom wheel size” and “Custom tire size.”
  • Optionally choose a “Wheels from (donor vehicle)” to compare stock-to-stock.
  • Review inner clearance and poke changes. Verify tire diameter difference is acceptable for you.
  • If any clearance looks tight, measure the car. Check caliper-to-spoke and barrel gaps physically during a test fit.

Next actions

Checklist

  • Confirm OEM specs in your manual or door jamb label.
  • Compare planned sizes in the calculator with “Installed on: 2018 Audi S8.”
  • Verify center bore 66.6 mm hub fit and M14 x 1.5 hardware compatibility.
  • Plan for TPMS transfer or programming if needed.
  • Test fit front first. Check caliper, barrel, and fender clearance at full lock and through suspension travel.
  • Torque to Audi spec using a calibrated wrench. Recheck after initial miles.
  • Schedule an alignment if you changed width, offset, or diameter.

Helpful tools

Wheel interchange calculator

Select Cars for Wheel Swap

Compare wheel compatibility between two vehicles

Wheels from (donor vehicle)

Installed on (your vehicle)